docs: def Sonnad_Goudar_2006(Re, eD):
      r'''Calculates Darcy friction factor using the method in Sonnad and Goudar
      (2006) [2]_ as shown in [1]_.
  
      .. math::
          \frac{1}{\sqrt{f_d}} = 0.8686\ln\left(\frac{0.4587Re}{S^{S/(S+1)}}\right)
  
      .. math::
          S = 0.1240\times\frac{\epsilon}{D}\times Re + \ln(0.4587Re)
  
      Parameters
      ----------
      Re : float
          Reynolds number, [-]
      eD : float
          Relative roughness, [-]
  
      Returns
      -------
      fd : float
          Darcy friction factor [-]
  
      Notes
      -----
      Range is 4E3 <= Re <= 1E8;  1E-6 <= eD <= 5E-2
  
      Examples
      --------
      >>> Sonnad_Goudar_2006(1E5, 1E-4)
      0.0185971269898162
  
      References
      ----------
      .. [1] Winning, H. and T. Coole. "Explicit Friction Factor Accuracy and
         Computational Efficiency for Turbulent Flow in Pipes." Flow, Turbulence
         and Combustion 90, no. 1 (January 1, 2013): 1-27.
         doi:10.1007/s10494-012-9419-7
      .. [2] 	Travis, Quentin B., and Larry W. Mays."Relationship between
         Hazen-William and Colebrook-White Roughness Values." Journal of
         Hydraulic Engineering 133, no. 11 (November 2007): 1270-73.
         doi:10.1061/(ASCE)0733-9429(2007)133:11(1270).
      '''
      S = 0.124*eD*Re + log(0.4587*Re)
      return (.8686*log(.4587*Re/S**(S/(S+1))))**-2